1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method and an image processing program.
2. Description of the Related Art
Conventionally, image diagnosis, whereby the internal structure of a human body can be directly observed, is performed by employing two dimensional images obtained by a CT (Computed Tomography) apparatus or an MRI (Magnetic Resonance Imaging) apparatus. Furthermore, volume rendering has recently begun to be employed, where three dimensional space is represented by voxels, the volume elements, which cuts the three dimensional space into small grids, based on a digital data which is generated by a collection of two dimensional images obtained by a CT apparatus or an MRI apparatus and any other medical imaging device. With this technique, internal human body structure can be visualized that is hardly understood only by studying each two dimensional image.
Ray casting is known as one volume rendering technique, where virtual ray is emitted to an object from a virtual starting point, and an image is formed on a virtual projection plane by the virtual ray reflected from the inside of the object, and whereby the three dimensional internal structure of the object is seen through. When having a diagnosis based on an image generated by ray casting, since the internal structure of a human body is extremely complicated, precision of the shape of the internal structure must be raised by reducing the sizes of voxels. However, as the precision is increased, the amount of data increases enormously, and an extended period of time is required to perform the calculation process for generating image data.
For an actual image diagnosis, a sequence of operation is repeated, where a target portion is displayed on a monitor screen, an affected part is observed in detail by repeating the operation such as gradually changing a display angle or gradually moving the display position, and finally the diagnostic information is reviewed in a report such as a diagnosis result.
In an image processing apparatus that performs this sequence of operation, a heavy load is imposed during the image data generating process, and a long time elapses before display data is obtained. However, once the data is displayed on a screen, no other processing is required but the apparatus simply waits to perform the next operation. As a consequence, an apparatus has been developed that effectively utilizes a period of time during which the imposed load is small, and that thereby reduces the time required for the acquisition of the next data to be displayed, as described in U.S. Pat. No. 6,182,133.
According to the display apparatus disclosed in U.S. Pat. No. 6,182,133, during a nonoperational period, the browser of a client computer obtains and stores a Web page, or its component in a local cache memory in advance, and the display apparatus is constructed as to visually notify a user by a visual sign via a graphical user interface that the new Web page has been extracted. During a period of time wherein the network load is low, an unused computer resource can be effectively utilized and a new Web page can be displayed quickly.
According to the display apparatus disclosed in U.S. Pat. No. 6,182,133, however, the browser of the client computer merely obtains and stores a Web page provided by a server computer in advance. A new image is neither created nor displayed.
Further, in image diagnosis, since a targeted human body differs in every diagnosis and an image is not provided in advance, and an image data for volume rendering image has to be generated after an instruction of the operator is input by calculation in accordance with the instruction. For example, when panning the display position, as shown in FIGS. 9A and 9B, after an instruction of the operator is input, a new image data is reconstructed by performing a complicated calculation using an enormous amount of data. Therefore, an extended period of time is required to display an image, and as is shown in FIG. 9B, a part of the image is darkened.
As a result, the conventional image processing apparatus not only contributes stress to the operator, but also degrades efficiency of diagnosis because an operation is halted until an image is displayed on a screen.